ガラモ葉上の貝類について

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Mollusks except opisthobranchs living on the thalli of a brown alga, Sargassum serratifolium, were studied at Mukaishima Island in the Inland Sea of Japan. A chiton, 27 prosobranchiate gastropods and 10 pelecypods were found. Among them, there are recognized two groups of different life forms : the genuine phytal species and the non-phytal ones. The former group, whose habitat is exclusively on sea weeds and sea-grasses, contains such prosobranchs as Cantharidus japonicus, Alcyna ocellata, Alvania concinna, A. sp., Diala varia, Diffalaba picta, Pleurotomitrella pleurotomoides, Zafra mitriformis and Crithe nanaoensis. On the other hand, some other gastropods and all pelecypod species occurred on the alga belong to the latter group, which usually inhabit rock surface or sediment bottom and utilized the algal thalli as a substratum by chance. The life cycles of the more abundant species were studied. The life span of phytal species such as D. picta and Z. mitriformis is less than one year, and the season of their larval settlement is when new generative laminae of the alga begin to grow. The subsequent rapid growth of these gastropods progresses keeping step with the expansion of the laminae, and they finish their reproduction and die out before the laminae are withered and washed away. On the other hand, the non-phytal species are not necessarily annual, and their life cycles have no relation to that of the alga. Thus, the pattern of the life cycles in the phytal group coincides well with that of the algal thalli, and it is suggested that such a remarkable coincidence has been acquired through evolutionary processes of mutual association between the phytal animals and their living habitats.
日本貝類学会の論文
1976-10-20

ガラモ葉上の貝類について

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